Helicopter



FIG. 1 is a side elevation of a helicopter, showing our new design;

FIG. 2 is an elevation of the side opposite that shown in FIG. 1;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevation thereof; and,

FIG. 6 is a rear elevation thereof.

Broken lines are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a helicopter, as shown and described. 